Adhesive Composition

ABSTRACT

An epoxy-based adhesive composition and the methods of manufacturing the same are provided. The adhesive composition provides excellent adhesion strength, peel strength and impact-resistant strength uniformly over a wide temperature range.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a national phase entry under 35 U.S.C. § 371of International Application No. PCT/KR2019/009236 filed Jul. 25, 2019,published in English, which claims priority from Korean PatentApplication No. 10-2018-0086344 filed on Jul. 25, 2018, all of which areincorporated herein by reference.

TECHNICAL FIELD

The present application relates to an adhesive composition.

BACKGROUND ART

Adhesives comprising epoxy resins, that is, epoxy resin-based adhesives,have high heat resistance and excellent adhesion strength and thus areused to bond or join various kinds of base materials. For example,recently, the epoxy resin-based adhesives have been used for metal-metaljoining or metal-plastic joining, and the like. In particular, when theepoxy resin-based adhesives are used in the automotive industry, thereis an advantage that the cost can be reduced and the weight of thevehicle body can be reduced by reducing the number of welds required formanufacturing vehicle body frames. As a result, there is a growingexpectation for application of epoxy resin adhesives in aerospace orwind power generation.

In consideration of accidents such as collisions, the epoxy resin-basedadhesives used for automobiles require not only excellent adhesionstrength but also impact-resistant strength. Then, these characteristicsshould be maintained uniformly over a wide range of temperatures inwhich automobiles are actually used, for example about −40 to 80° C.However, the epoxy resin-based adhesives according to the prior art havea problem that they do not provide sufficient strength for lowtemperature conditions such as −40° C.

DISCLOSURE Technical Problem

It is one object of the present application to provide an epoxyresin-based adhesive composition.

It is another object of the present application to provide an adhesivecomposition that provides excellent adhesion strength, impact strengthand shear strength over a wide temperature range.

The above objects and other objects of the present application can allbe solved by the present application described in detail below.

Technical Solution

In one example of the present application, the present applicationrelates to an adhesive composition comprising an epoxy-based resin. Theadhesive composition may be used to bond homogeneous or heterogeneousbase materials after curing. For example, the base material may comprisea metal component or a plastic component, whereby the adhesivecomposition may be used for metal-metal joining, metal-plastic joiningor plastic-plastic joining, and the like. A joining body (hereinafter,may be referred to as a composite or a structure) of such a basematerial can be used, for example, as a component of an automobile orthe like.

In the present application, the adhesive composition may comprise a) oneor more epoxy resins, (b) acrylic crosslinked particles containing analkyl (meth)acrylate unit and a unit of a monomer having an alkyleneoxide group, (c) a core-shell rubber in the form of secondary particlesin which two or more core-shell rubbers in the form of primary particlesare aggregated, (d) one or more epoxy curing agents and (e) a urethaneresin having a polyether structure. The adhesive composition of thepresent application comprising all of these configurations can provideexcellent adhesion strength, impact-resistant strength and shearstrength uniformly for a structure formed using the cured product of theadhesive composition from a low temperature such as −40° C. to a hightemperature such as 80° C.

(a) Epoxy Resin

When all the (a) to (e) configurations are included, the specificstructure of the epoxy resin used for the adhesive composition of thepresent application is not particularly limited. For example, the epoxyresin may be an epoxy resin having a saturated or unsaturated group, andmay be an epoxy resin containing a cyclic structure or an acyclicstructure. In addition, the specific kind of the epoxy resin used in thepresent application is not particularly limited either. For example, theepoxy resin may include a bisphenol-based epoxy resin such as bisphenolA series or bisphenol F series; a novolac-based epoxy resin; or anoxazolidone-containing epoxy resin, and the like.

In one example, the epoxy resin may include one or more selected from abisphenol A-based epoxy resin and a bisphenol F-based epoxy resin. Forexample, the trade name YD-128, YDF-170 or YD-011 from Kukdo Chemical,and the like can be used.

In one example, the epoxy resin (a) may include an epoxy resin having anepoxy equivalent of less than 300. Specifically, the equivalent upperlimit of the epoxy resin having an epoxy equivalent of less than 300 maybe, for example, 280 or less, 260 or less, 240 or less, 220 or less, or200 or less. Although not particularly limited, the equivalent lowerlimit of the epoxy resin having an epoxy equivalent of less than 300 maybe, for example, 100 or more, 110 or more, 120 or more, 130 or more, 140or more, or 150 or more. If the equivalent range is satisfied, thespecific structure or type of the epoxy resin having an epoxy equivalentof less than 300 is not particularly limited.

In one example, the adhesive composition may comprise two or more epoxyresins that one or more features selected from an epoxy equivalent, amolecular weight or a viscosity are different from each other.

In one example, the adhesive composition may comprise two or more epoxyresins having different epoxy equivalents from each other. The epoxyequivalents of the two or more epoxy resins may be, for example, in arange of 120 to 700, and they may have equivalents different from eachother. That is, the adhesive may comprise an epoxy resin mixture (a) inwhich two or more resins having different equivalents from each otherare mixed.

In one example, the epoxy resin mixture (a) may further comprise one ormore epoxy resins having an epoxy equivalent of 300 or more. Forexample, the epoxy equivalent of the epoxy resin may be 320 or more, 340or more, 360 or more, 380 or more, 400 or more, 420 or more, 440 ormore, 460 or more, 480 or more, 500 or more, 520 or more, 540 or more,560 or more, 580 or more, or 600 or more. Although not particularlylimited, the epoxy equivalent upper limit of the resin may be 650 orless, 640 or less, 630 or less, or 620 or less.

In one example, the adhesive composition may comprise a bisphenolA-based epoxy resin as the epoxy resin having an epoxy equivalent ofless than 300. The specific structure of the used epoxy resin is notparticularly limited as long as the equivalent is satisfied.

In another example, the adhesive composition may comprise a bisphenolA-based epoxy resin as the epoxy resin having an epoxy equivalent of 300or more. The specific structure of the used epoxy resin is notparticularly limited as long as the equivalent is satisfied.

In one example, the adhesive composition may comprise a bisphenolF-based resin as the epoxy resin having an epoxy equivalent of less than300. The specific structure of the used epoxy resin is not particularlylimited as long as the equivalent is satisfied.

In another example, the adhesive composition may further comprise abisphenol F-based resin as the epoxy resin having an epoxy equivalent of300 or more. The specific structure of the used epoxy resin is notparticularly limited as long as the equivalent is satisfied.

In one example, the adhesive composition may comprise both of thebisphenol A-based resin and F-based resin satisfying the equivalentrange.

When the epoxy equivalent increases, the crosslinking density maygenerally decrease while the viscosity increases, and the strengthobserved after the composition has cured may also be somewhat poor. Inaddition, when the epoxy equivalent decreases, there is a problem thatcannot fully expect the effect of using the epoxy-based adhesive.However, when the resins having a predetermined epoxy equivalent asabove are mixed and used, there is an advantage that can solve the aboveproblems.

In one example, the adhesive composition may comprise an epoxy resinhaving an epoxy equivalent of less than 300 in an amount of 15 parts byweight or more relative to the total content of the adhesivecomposition. For example, the content of the epoxy resin having an epoxyequivalent of less than 300 may be 20 parts by weight or more, 25 partsby weight or more, 30 parts by weight or more, 35 parts by weight ormore, 40 parts by weight or more, 45 parts by weight or more, or 50parts by weight or more. In addition, although not particularly limited,the content upper limit of the epoxy resin having an epoxy equivalent ofless than 300 may be, for example, 65 parts by weight or less, or 60parts by weight or less.

In one example, the adhesive composition may comprise an epoxy resinhaving an epoxy equivalent of 300 or more in an amount of 1 part byweight relative to the total content of the adhesive composition.Specifically, the content of the epoxy resin having an epoxy equivalentof 300 or more may be 2 parts by weight or more, 3 parts by weight ormore, 4 parts by weight or more, 5 parts by weight or more, 6 parts byweight or more, 7 parts by weight or more, 8 parts by weight or more, 9parts by weight or more, or 10 parts by weight or more. In addition,although not particularly limited, the content upper limit of the epoxyresin having an epoxy equivalent of 300 or more may be, for example, 15parts by weight or less, or 10 parts by weight or less.

In one example, the epoxy resin or the epoxy resin mixture may be usedin an amount of 15 parts by weight or more, 20 parts by weight or more,25 parts by weight or more, 30 parts by weight or more, 35 parts byweight or more, or 40 parts by weight or more, relative to the totalcontent of the adhesive composition. The upper limit thereof is notparticularly limited, but may be, for example, 80 parts by weight orless, 75 parts by weight or less, 70 parts by weight or less, 65 partsby weight or less, 60 parts by weight or less, 55 parts by weight orless, or 50 parts by weight or less.

In the present application, the adhesive composition may comprise a monoepoxy resin. In the present application, the mono epoxy resin may mean acomponent having one epoxy functional group in the molecule. The monoepoxy resin is capable of lowering the viscosity of the adhesive, and isadvantageous in improving wettability, impact characteristics oradhesion (peeling) characteristics by adjusting the crosslinkingdensity.

In another example, the mono epoxy resin may be used in an amount of 10parts by weight or less relative to the total content of the adhesivecomposition. Specifically, the content of the mono epoxy resin may be,for example, 9 parts by weight or less, 8 parts by weight or less, 7parts by weight or less, 6 parts by weight or less, or 5 parts by weightor less. The lower limit is not particularly limited, but may be, forexample, 0.5 parts by weight or more.

(b) Acrylic Crosslinked Particles

The adhesive composition may further comprise acrylic crosslinkednanoparticles. The acrylic crosslinked nanoparticles may be mixed withcore-shell rubber particles to be uniformly dispersed in a matrix resin,and contribute to improving impact resistance due to high-specificsurface area.

In one example, the acrylate-based crosslinked particles may comprise apolymer of an alkyl (meth)acrylate, or a copolymer of an alkyl(meth)acrylate and a heterogeneous monomer. In one example, as theheterogeneous monomer, a vinyl-based monomer having an alkylene oxidegroup or a polyfunctional acrylate monomer can be used. When thecrosslinked particles comprise a copolymer of an alkyl (meth)acrylateand a heterogeneous monomer, the copolymer may comprise 80 to 95 partsby weight of an alkyl (meth)acrylate-derived unit.

In one example, the crosslinked particles may comprise an alkyl(meth)acrylate unit and a polyfunctional acrylate monomer unit. In thiscase, the acrylic resin may be crosslinked by the polyfunctionalmonomer.

In one example, as the polyfunctional acrylate monomer,trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate,diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate,decaethylene glycol di(meth)acrylate, pentadecaethylene glycoldi(meth)acrylate, pentacontahectaethylene glycol di(meth)acrylate,pentaerythritol tetra(meth)acrylate, 1,3-butylene di(meth)acrylate,allyl (meth)acrylate, and the like can be used.

In one example, the acrylic crosslinked particles may have an averageparticle diameter in a range of 10 nm to 200 nm. In the presentapplication, the “particle diameter” may be used to mean a diameter of aparticle that is spherical or ellipsoidal, and may mean the length ofthe longest dimension when the particle shape is not completelyspherical or ellipsoidal. The ‘average’ means the diameter of theparticle with 50% of the cumulative weight in the particle sizedistribution curve for the relevant particles. The particlediameter-related features may be measured using known equipment, and forexample, dynamic lighting scattering or laser diffraction equipment andthe like may be used to identify the particle diameter-related features.In the case of having the average particle diameter as above, the impactstrength can be improved even with a relatively small amount withoutdeteriorating other physical properties. Unless specifically defined,the particle diameter of the particles or particle size of the particlesmay be used in the sense of the average particle diameter to bedescribed below.

In one example, the acrylic crosslinked particles may be included in anamount of 15 parts by weight or less relative to the total content ofthe adhesive composition. Specifically, the acrylic crosslinkedparticles may be included in an amount of 14 parts by weight, 13 partsby weight, 12 parts by weight, 11 parts by weight, or 10 parts by weightor less, relative to the total content of the adhesive composition.Although not particularly limited, the acrylic crosslinked particles maybe included in an amount of 1 part by weight or more, 2 parts by weightor more, 3 parts by weight or more, 4 parts by weight or more, or 5parts by weight or more.

(c) Rubber

The adhesive composition comprises a core-shell rubber in the form ofsecondary particles in which two or more core-shell rubbers in the formof primary particles are aggregated.

In the present application, the “core-shell rubber” may mean aparticulate (solid) material having a rubber component in a core portionand having a structure in which a shell material is grafted orcrosslinked to the core.

Then, in the present application, the “core-shell rubber in the form ofprimary particles” may mean each unit body having the core-shellstructure, and the “core-shell rubber in the form of secondaryparticles” may mean an aggregate (or conglomerate) formed by clumpingtwo or more core-shell rubbers (particles) in the form of primaryparticles together. The core-shell rubbers may be dispersed and presentin the adhesive composition.

In one example, the core-shell rubber particles in the primary form andthe core-shell rubber particles in the secondary form can be preparedaccording to the methods described in the following examples. In thiscase, the aggregated rubbers in the secondary form produced by apolymerization reaction can be separated into smaller aggregated rubbersthrough a kneader such as a planetary mixer. In one example, all of theaggregated particles may not be separated in the form of completeprimary particles, and some of the secondary particles may be separatedinto primary particles and present in a mixed form of primary andsecondary particles. For example, the weight ratio of the primaryparticles may be 50 wt % or less, 40 wt % or less, 30 wt % or less, 20wt % or less, 10 wt % or less, 5 wt % or less, 4 wt % or less, 3 wt % orless, 2 wt % or less, 1 wt % or less, or 0.5 wt % or less, relative tothe total content of the core-shell rubbers. In one example, the weightratio of the primary particles may be substantially 0 wt %.Alternatively, the weight ratio of the primary particles may be, forexample, 0.01 wt % or more, 0.1 wt % or more, or 1 wt % or more.

In another example, the core-shell rubber particles in the primary formand the core-shell rubber particles in the secondary form may beprepared through a separate process.

The core may comprise a polymer of a diene-based monomer, or maycomprise a copolymer of a diene-based monomer and a heterogeneousmonomer component (not diene-based). Although not particularly limited,for example, butadiene or isoprene may be used as the diene-basedmonomer.

In one example, the core may be a butadiene-based core. For example, thecore may comprise a polymer of butadiene. In addition, the core maycomprise a copolymer of butadiene and another ethylenically unsaturatedmonomer. The ethylenically unsaturated monomer used upon core formationcan be exemplified by a vinyl-based aromatic monomer,(methyl)acrylonitrile, an alkyl (meth)acrylate, and the like, but is notparticularly limited thereto.

In one example, when the alkyl (meth)acrylate is additionally used incore formation, a different kind of alkyl (meth)acrylate from an alkyl(meth)acrylate used for shell formation, which is described below, canbe used in the core.

The shell grafted or crosslinked to the core may comprise an alkyl(meth)acrylate unit. The fact that the shell comprises an alkyl(meth)acrylate unit means that an alkyl (meth)acrylate monomer can beused upon forming a shell polymer that is crosslinked or grafted to thecore. In one example, as the alkyl (meth)acrylate, a lower alkyl(meth)acrylate having an alkyl group having 1 to 6 carbon atoms, such asmethyl methacrylate, ethyl methacrylate or t-butyl methacrylate can beused, without being limited to the above-listed monomers.

The shell may further comprise a vinylidene-based monomer unit. Forexample, it may further comprise a unit of an aromatic vinyl monomersuch as styrene, vinyl acetate or vinyl chloride. Although notparticularly limited, in one example, the shell may comprise an alkyl(meth)acrylate unit and an aromatic vinyl monomer unit.

In one example, the core and shell may have a predetermined glasstransition temperature (Tg). For example, the glass transitiontemperature (Tg) lower limit of the core may be −60° C. or more, −50° C.or more, or −40° C. or more. Although not particularly limited, theglass transition temperature upper limit of the core may be −20° C. orless, −25° C. or less, −30° C. or less, or −35° C. or less. In addition,the shell may have, for example, a glass transition temperature (Tg) of50° C. or more, 60° C. or more, or 70° C. or more. Although notparticularly limited, the glass transition temperature upper limit ofthe shell may be 120° C. or less. The glass transition temperature canbe measured according to a known method, and for example, can bemeasured using differential scanning calorimetry (DSC).

In one example, the core-shell rubber in the form of primary particlesmay have a ratio of the core particle diameter to the total core-shellparticle diameter (=thickness ratio of the core in the core-shell, R) of0.80 or more.

In the present application, the “particle diameter” may be used to meana diameter of a particle-shaped (for example, spherical or ellipsoidal)core-shell rubber or the configuration thereof, and may mean the lengthof the longest dimension when the shape of the core-shell rubber is notcompletely spherical or ellipsoidal. The particle diameter-relatedfeatures may be measured using known equipment, and for example, dynamiclighting scattering or laser diffraction equipment and the like may beused to identify the particle diameter-related features. Unlessspecifically defined, the particle diameter of the particles or particlesize of the particles may be used in the sense of the average particlediameter to be described below.

For example, the ratio of the core particle diameter to the totalcore-shell particle diameter may be 0.81 or more, 0.82 or more, 0.83 ormore, 0.84 or more, 0.85 or more, 0.86 or more, 0.87 or more, 0.88 ormore, 0.89 or more, or 0.90 or more. The upper limit of the ratio maybe, for example, 0.99, and specifically, may be 0.98 or less, 0.97 orless, 0.96 or less, 0.95 or less, 0.94 or less, 0.93 or less, or 0.92 orless. In the case of commercialized core-shell products, they do notsatisfy the above range in many cases, so that the impact absorptionfunction by the rubber is not sufficient, but the core-shell rubbersatisfying the above range can sufficiently absorb the impact applied tothe structure. In particular, when the ratio of the core exceeds 0.99,it becomes difficult for the shell to surround the core part while thethickness of the shell becomes thin, whereby a decrease in compatibilitywith the epoxy resin or a decrease in dispersibility may occur. Inaddition, when the ratio of the core is less than 0.8, the effect ofimproving the impact strength is insufficient.

For example, when the core-shell rubber in the form of primary particleshas an average particle diameter of 250 nm or more, 260 nm or more, 270nm or more, 280 nm or more, 290 nm or more, or 300 nm or more, and forexample, the upper limit thereof is 600 nm or less or 500 nm or less,specifically, 450 nm or less, 440 nm or less, 430 nm or less, 420 nm orless, 410 nm or less, or 400 nm or less, the core-shell rubber in theform of primary particles may have a size that can satisfy the aboveratio (R). At this time, the ‘average particle diameter” means thediameter that the particle with 50% of the cumulative weight (mass) inthe particle size distribution curve has (passes). For example, the coreof the core-shell rubber in the form of primary particles may have anaverage particle diameter of 180 nm or more, 200 nm or more, 220 nm ormore, 240 nm or more, 260 nm or more, 280 nm or more, 300 nm or more,and the upper limit thereof may be, for example, 500 nm or less, 495 nmor less, 490 nm or less, specifically, 450 nm or less, 400 nm or 350 nmor less. In the case of commercialized core-shell products, the size andratio (R) of the corresponding particle diameter do not satisfy theabove range in many cases, so that the impact absorption function by therubber is not sufficient.

In another example, the core-shell rubber in the form of primaryparticles may have an average particle diameter of 250 nm or less. Inthis case, the lower limit thereof may be, for example, 10 nm or more,20 nm or more, or 30 nm or more. Even in the case of having such aparticle diameter, the core-shell rubber in the form of primaryparticles may have the ratio (R) of the core particle diameter to thetotal core-shell particle diameter satisfying the above range. In thecase of commercialized core-shell products, the size of thecorresponding particle diameter does not satisfy the above range in manycases, so that the impact absorption function by the rubber is notsufficient.

Also, in the present application, the core-shell rubber may have apredetermined particle size distribution.

In one example, the core-shell rubber in the form of primary particlesmay have a diameter of D₁₀ in the particle diameter distribution, thatis, a diameter up to cumulative 10% particles on the basis of weight(mass), from the smaller side of the particle diameters by the particlesize distribution measurement, in a range of 180 to 220 nm.

In another example, the core-shell rubber in the form of primaryparticles may have a diameter of D₅₀ in the particle diameterdistribution, that is, a diameter up to cumulative 50% particles on thebasis of weight (mass), from the smaller side of the particle diametersby the particle size distribution measurement, in a range of 250 to 350nm.

In another example, the core-shell rubber in the form of primaryparticles may have a diameter of D₉₀ in the particle diameterdistribution, that is, a diameter up to cumulative 90% particles on thebasis of weight (mass), from the smaller side of the particle diametersby the particle size distribution measurement, in a range of 450 to 510nm.

In one example, the core-shell rubber in the form of primary particlesmay have a particle size distribution width of 2.0 or less or 1.5 orless obtained by the following equation 1. The lower limit thereof isnot particularly limited, which may be, for example, 0.5 or more, 0.6 ormore, 0.7 or more, 0.8 or more, 0.9 or more, or 1.0 or more.

(D ₉₀ −D ₁₀)/(D ₅₀)  [Equation 1]

As described above, when the core-shell rubber having a narrow particlesize distribution width is used, it is advantageous to uniformly secureexcellent adhesion strength, peel strength, and impact-resistantstrength in a wide temperature range.

Such particle diameter characteristics can be obtained through, forexample, a method of appropriately adjusting the type or content ofmonomers used upon core or shell formation, or a method of dividing themonomers into several stages to be introduced or appropriately adjustingthe polymerization time of the core or shell or other polymerizationconditions, and the like.

In one example, the number of primary particles aggregated for secondaryparticle formation is not particularly limited. For example, the primaryparticles may be aggregated to form secondary particles, so that thecore-shell rubber conglomerate (aggregate), that is, the secondaryparticles may have a diameter in a range of 0.1 to 10 μm. In oneexample, the core-shell rubber (aggregated particles) in the form ofsecondary particles, which has undergone a kneading process through akneader such as a planetary mixer after polymerization, may have a sizeof 2 μm or less, 1.5 μm or less, 1 μm or less, or 0.5 μm or less. Inrelation to the secondary particles, the size may be used in the sensecorresponding to the particle diameter or the size of the longestdimension as described above.

In one example, the average particle diameter of the core-shell rubberin the form of secondary particles may be 1.5 μm or less, or 1 μm orless. Specifically, the average particle diameter of the core-shellrubber may be 900 nm or less, 800 nm or less, 700 nm or less, or 600 nmor less. Although not particularly limited, the average particlediameter lower limit of the core-shell rubber in the form of secondaryparticles may be 100 nm or more, 200 nm or more, 300 nm or more, 400 nmor more, or 500 nm or more.

The core-shell rubber in the form of secondary particles satisfying theabove-described characteristics may be included in an amount of 5 partsby weight or more based on the total content of the adhesivecomposition. Specifically, the lower limit of the content may be 6 partsby weight or more, 7 parts by weight or more, 8 parts by weight or more,9 parts by weight or more, or 10 parts by weight or more. In addition,the content of the core-shell rubber conglomerate may be 35 parts byweight or less. Specifically, the upper limit of the content may be 34parts by weight or less, 33 parts by weight or less, 32 parts by weightor less, 31 parts by weight or less, or 30 parts by weight or less, andmore specifically, may be 25 parts by weight or less, or 20 parts byweight or less. When it is used less than the content, the impactstrength improvement effect is not sufficient, and when it is used inexcess of the above range, it is not preferable because shear strengthand high-temperature impact strength may be lowered.

In one example, the adhesive composition may further comprise a liquidrubber.

In one example, the liquid rubber may be a configuration having an epoxygroup at the end of the liquid rubber, which is a homopolymer of adiene-based monomer or a copolymer of a diene-based monomer and aheterogeneous monomer. That is, the liquid rubber may be an epoxyterminated liquid rubber.

For example, the liquid rubber may comprise a homopolymer or copolymerhaving repeating units derived from butadiene or isobutadiene. In theliquid rubber, for example, a copolymer of butadiene or isobutadiene andan acrylate and/or an acrylonitrile may be included.

In one example, the content of the liquid rubber may be the same as thatof the above-described core-shell rubber.

In one example, the adhesive composition may comprise at least 5 partsby weight or 10 parts by weight or more of a rubber (core-shell rubberand/or liquid rubber) based on the total content of the adhesivecomposition. For example, when the adhesive composition comprises onlythe core-shell rubber, the adhesive composition may comprise at least 5parts by weight or 10 parts by weight or more of the core-shell rubberbased on the total content of the adhesive composition. Alternatively,when the adhesive composition comprises both the core-shell rubber andthe liquid rubber, the adhesive composition may comprise at least 5parts by weight or 10 parts by weight or more of the core-shell rubberand the liquid rubber based on the total content of the adhesivecomposition. Even in such a case, the rubber components may be used inan amount of 35 parts by weight or less, in consideration of shearstrength and high-temperature impact strength. In one example, theadhesive composition may comprise a rubber (core-shell rubber and/orliquid rubber) in an amount of 10 parts by weight or more, 12 parts byweight or more, or 14 parts by weight or more, and 30 parts by weight orless, 25 parts by weight or less, or 22 parts by weight or less, basedon the total content of the adhesive composition.

(d) Epoxy Curing Agent

The adhesive composition may comprise a predetermined curing agent sothat it can be cured at a temperature of about 80° C. or more, or about100° C. or more. If the curing can occur in the above temperature range,the type of the curing agent is not particularly limited. For example,as the curing agent, a dicyandiamide, a melamine, a diallyl melamine, aguanamine (e.g. acetoguanamine, benzoguanamine), an aminotriazole(3-amino-1,2,4-triazole), a hydrazide (adipic acid dihydride, stearicacid dihydrazide, isophthalic acid dihydrazide), a cyanoacetamide or anaromatic polyamine (e.g.: diaminodiphenylsulfone), and the like can beused.

Although not particularly limited, the curing agent may be used in anamount of, for example, 1 part by weight or more, 2 parts by weight ormore, 3 parts by weight or more, or 4 parts by weight or more, based onthe total content of the adhesive composition. Although not particularlylimited, the content upper limit of the curing agent may be 15 parts byweight or less, 14 parts by weight or less, 13 parts by weight or less,12 parts by weight or less, 11 parts by weight or less, or 10 parts byweight or less.

(e) Urethane Resin

The urethane resin used in the present application may have a structure(capping structure) in which at least one of the isocyanate groups whichare terminals of the urethane resin is terminated with a predeterminedcompound, as described below.

The urethane resin may contain an isocyanate unit and a polyether polyolunit. In the present application, the fact that the urethane resincomprises predetermined units may mean a state where in a resinstructure (main chain or side chain) formed by reaction of one or morecompounds, the compounds are polymerized and simultaneously the unitsderived therefrom are included in the resin structure.

The specific kind of isocyanate used in the urethane resin is notparticularly limited, and a known aromatic or non-aromatic isocyanatemay be used. In a non-limiting example, the isocyanate can benonaromatic. That is, upon forming the modified urethane resin, anisocyanate of aliphatic or alicyclic series may be used. In the case ofusing the non-aromatic isocyanate, impact resistance, or viscositycharacteristics of the adhesive composition may be improved.

The kind of the usable non-aromatic isocyanate is not particularlylimited. For example, an aliphatic polyisocyanate or its modifiedproducts can be used. Specifically, an aliphatic polyisocyanate such ashexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysinediisocyanate, norbornane diisocyanate methyl, ethylene diisocyanate,propylene diisocyanate or tetramethylene diisocyanate; an alicyclicpolyisocyanate such as transcyclohexane-1,4-diisocyanate, isophoronediisocyanate, bis(isocyanatemethyl) cyclohexane diisocyanate ordicyclohexylmethane diisocyanate; or a carbodiimide-modifiedpolyisocyanate or isocyanurate-modified polyisocyanate of at least oneof the foregoing; and the like can be used. In addition, a mixture oftwo or more of the above-listed compounds can be used.

In one example, the polyol may be a polyol having an OH equivalent of300 or more. For example, the OH equivalent lower limit of the polyolmay be 400 or more, 500 or more, 600 or more, 700 or more, 800 or more,or 900 or more. The OH equivalent upper limit of the polyol is notparticularly limited, but may be, for example, 2,000 or less, 1,900 orless, 1,800 or less, 1,700 or less, 1,600 or less, 1,500 or less, 1,400or less, 1,300 or less, 1,200 or less, or 1,100 or less. When theequivalent range is satisfied, it is advantageous to improveimpact-resistant characteristics, adhesion strength characteristics andpeeling characteristics of the adhesive.

The kind of the polyol is not particularly limited as long as theequivalent is satisfied. For example, a tetrafunctional polyol such aspentaerythritol; a trifunctional polyol such as glycerin ortrimethylolpropane; or a bifunctional polyol such as glycol may be used.In one example, a polyalkylene glycol may be used as the polyol, withoutbeing particularly limited thereto. Specifically, for example,polypropylene glycol may be used as the polyalkylene glycol.

In one example, the urethane resin may comprise a branched polyetherpolyol unit, and a non-aromatic isocyanate unit.

In one example, the polyol may be branched polypropylene glycol. Thebranched polypropylene means that the polypropylene backbone isconfigured to have side chains, which may be distinguished from thelinear shape, that is, the case where the polypropylene repeating unitdoes not have side chains. For example, the branched polypropylene hasbranches in which a-olefins, such as ethylene, 1-butene, 1-hexene or4-methyl-1-pentene, are incorporated (copolymerized) into thepolypropylene backbone. That is, in one example of the presentapplication, the polyol may have a branched polypropylene unit. When thebranched polypropylene glycol is used, it is advantageous for strengthimprovement.

As mentioned above, the urethane resin may have a structure in which oneor more of its isocyanate ends are terminated by a predeterminedcompound. The so-called capping method of the isocyanate end in theurethane resin is not particularly limited. Known techniques can beused. For example, a polymer or prepolymer, which is derived from anether-based polyol, having urethane groups in urethane chains and havingisocyanate groups at their ends is prepared, where the isocyanate endsof the urethane can be capped through a compound having an activehydrogen group at all or part of the isocyanate groups. In anotherexample, upon preparing the urethane resin, a method of cappingsimultaneously with polymerization by introducing a compound capable ofcapping the isocyanate ends together may be used. The kind of thecompound which is capable of capping isocyanate ends is not specificallylimited, and for example, an amine-based compound, a phenol-basedcompound, an oxime-based compound, or a bisphenol-based compound can beused.

In one example, the urethane resin may have a weight average molecularweight (Mw) of 3,000 to 40,000. The weight average molecular weight maybe a polystyrene conversion molecular weight measured by GPC. Morespecifically, the lower limit of the weight average molecular weight ofthe urethane resin may be 3,000 or more, 3,500 or more, 4,000 or more,4,500 or more, 5,000 or more, 5,500 or more, 6,000 or more, 6,500 ormore, 7,000 or more, 7,500 or more, 8,000 or more 8,500 or more, or9,000 or more. Although not particularly limited, the upper limit of theweight average molecular weight of the urethane resin may be 35,000 orless, or 30,000 or less. When the above range is satisfied, it ispossible to provide advantageous physical properties to the adhesive.The urethane resin may have a molecular weight controlled using abranching agent, a chain extender or the like upon its manufacture, andmay also have a linear structure or a branched structure. In the case ofthe branched structure, it is appropriate to polymerize the urethanewithout using a chain extender, which is advantageous for obtaining anappropriate molecular weight. When polypropylene glycol is used as thepolyol, the degree of contribution to improving the impact strength ofthe urethane resin having a branched structure may be higher.

In one example, the adhesive composition may comprise 5 parts by weightor more of the modified urethane resin based on the content of theentire adhesive composition. Specifically, the content of the modifiedurethane resin may be 6 parts by weight or more, 7 parts by weight ormore, 8 parts by weight or more, 9 parts by weight or more, or 10 partsby weight or more. Although not particularly limited, the content upperlimit of the urethane resin may be, for example, 25 parts by weight orless. More specifically, the urethane resin may be used in an amount of20 parts by weight or less, 19 parts by weight or less, 18 parts byweight or less, 17 parts by weight or less, 16 parts by weight or less,or 15 parts by weight or less. When the urethane resin is used in anamount of less than the above range, the impact strength improvement isnot sufficient, and when it is used in an amount of more than the aboverange, there is a problem that shear strength is lowered andhigh-temperature impact strength is lowered.

(f) Other Components

The adhesive composition may comprise a catalyst to control the rate andtemperature of the curing reaction by the curing agent. The type of thecatalyst is not particularly limited, and various kinds of knowncatalysts may be appropriately used.

In one non-limiting example, as the catalyst, urea series such asp-chlorophenyl-N,N-dimethylurea, 3-phenyl-1,1-dimethylurea or3,4-dichlorophenyl-N,N-dimethylurea; tertiary acrylics; amines such asbenzyldimethylamine; piperidine or derivatives thereof; or imidazolederivatives may be used.

Although not particularly limited, the catalyst may be used, forexample, in an amount of 0.1 parts by weight or more, 0.2 parts byweight or more, 0.3 parts by weight or more, or 0.4 parts by weight ormore, based on the total content of the adhesive composition. Althoughnot particularly limited, the upper limit of the catalyst content may be2 parts by weight or less.

In one example, the adhesive composition may further comprise aparticulate inorganic filler, that is, inorganic particles. When theinorganic filler is used, it is possible to adjust the mechanicalproperties, rheological properties and the like of the adhesive. Theform of the inorganic filler may be rectangular, spherical, platy oracicular, which is not particularly limited.

As the inorganic filler, for example, calcium oxide, quartz powder,alumina, calcium carbonate, calcium oxide, aluminum hydroxide, magnesiumcalcium carbonate, barite, hydrophilic or hydrophobic silica particles,or aluminum magnesium calcium silicate can be used. When silicaparticles are used, it is more preferable that they have hydrophobicity.

Although not particularly limited, the inorganic filler may be used inan amount of, for example, 1 part by weight or more, 2 parts by weightor more, 3 parts by weight or more, or 4 parts by weight or more, basedon the total content of the adhesive composition. Although notparticularly limited, the upper limit of the inorganic filler contentmay be 15 parts by weight or less, or 10 parts by weight or less.

In one example, the composition may further comprise various kinds ofadditives. For example, known plasticizers, reactive or non-reactivediluents, coupling agents, fluidity modifiers, thixotropic agents,colorants, and the like may further be included in the adhesivecomposition. The specific kind of the additive is not particularlylimited, and known materials or commercial products may be used withoutlimitation.

Although not particularly limited, the additive may be used in an amountof, for example, 0.1 parts by weight or more, 1 part by weight or more,2 parts by weight or more, or 3 parts by weight or more, based on thetotal content of the adhesive composition. Although not particularlylimited, the upper limit of the additive content may be 15 parts byweight or less, 14 parts by weight or less, 13 parts by weight or less,12 parts by weight or less, 11 parts by weight or less, or 10 parts byweight or less.

In another example of the present application, the present applicationrelates to a structure comprising a cured product of the adhesivecomposition. The structure may comprise a base material and a curedproduct of the adhesive composition cured after being applied on thebase material. The base material may comprise a metal component, aplastic component, wood, a glass fiber-containing base material, and thelike.

In one example, the structure may have a form in which two or more basematerials are bonded via the cured product. For example, the structuremay have a form in which a metal and a metal are bonded via the curedproduct, a form in which a metal and a plastic are bonded via the curedproduct, or a form in which a plastic and a plastic are bonded via thecured product. The structure can be used as a structural material foraerospace, wind power generation, ships or automobiles.

In another example of the present application, the present applicationrelates to a method for producing a structure. The method may comprisesteps of applying a composition having a configuration as describedabove on a surface of a base material and curing the composition appliedto the surface of the base material. The application may be performedsuch that physical contact between the base material and the adhesivecomposition occurs.

The method of applying the adhesive composition to the surface of thestructure is not particularly limited. For example, jet spraying methodssuch as swirl or streaming, or mechanical application by an extrusionmethod can be used. The application may be made to one or more basematerials to be bonded.

The curing temperature is not particularly limited. For example, thecuring may be performed at 80° C. or more, or 100° C. or more. Althoughnot particularly limited, considering heat-resistant stability, it ispreferable to perform the curing at a temperature of 220° C. or less.

Advantageous Effects

According to one example of the present application, an adhesivecomposition providing excellent adhesion strength, peel strength andimpact-resistant strength uniformly over a wide temperature range can beprovided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows the particle size distribution of the core-shell rubbers(in the form of primary particles) prepared according to one embodimentof the present application. The horizontal axis means particlediameters, and the vertical axis means relative numbers of rubbers.

FIG. 2 is an image taken to the appearance that the core-shell rubbersprepared according to one embodiment of the present application aredispersed in an epoxy resin.

DETAILED DESCRIPTION

Hereinafter, the present application will be described through examplesand comparative examples. However, the scope of the present applicationis not limited by the scope set forth below.

PRODUCTION EXAMPLES Production Example 1: Production of Core-ShellRubber Assembly

First step (production of core): 70 parts by weight of ion-exchangedwater, 60 parts by weight of 1,3-butadiene as a monomer, 1.0 part byweight of sodium dodecylbenzene sulfonate as an emulsifier, 0.85 partsby weight of calcium carbonate, 0.28 parts by weight of tertiary dodecylmercaptan and 0.28 parts by weight of persulfate potassium as aninitiator were introduced into a nitrogen-substituted polymerizationreactor, and reacted at 75° C. until a polymerization conversion ratiowas 30 to 40%. Thereafter, 0.3 parts by weight of sodium dodecylbenzenesulfonate was introduced thereto, 20 parts by weight of 1,3-butadienewas further introduced thereto, and the temperature was raised to 80° C.to terminate the reaction at the time when the polymerization conversionratio was 95%. The produced polymer had a latex gel content of 73%. Atthis time, the rubber latex was coagulated with a dilute acid or a metalsalt, and then washed, dried in a vacuum oven at 60° C. for 24 hours,and 1 g of the resulting rubber was placed in 100 g of toluene andstored in a dark room at room temperature for 48 hours, and then thelatex gel content was measured by separating the sol and the gel.

Second step: 70 parts by weight of the produced rubber latex was putinto a closed reactor, and the temperature of the reactor filled withnitrogen was raised to 75° C. Thereafter, 0.1 parts by weight of sodiumpyrophosphate, 0.2 parts by weight of dextrose and 0.002 parts by weightof ferrous sulfide were introduced into the reactor in a lump.

In a separate mixing device, 25.5 parts by weight of methylmethacrylate, 4.5 parts by weight of styrene, 0.5 parts by weight ofsodium dodecylbenzene sulfonate as an emulsifier, 0.1 parts by weight ofcumene hydroperoxide and 20 parts by weight of ion-exchanged water weremixed to prepare a monomer emulsion.

To the reactor to which the rubber latex had been introduced, theemulsion was continuously added over 3 hours, and then, after 30minutes, 0.03 parts by weight of hydroperoxide was added and aged at thesame temperature for 1 hour to terminate the reaction at the time whenthe polymerization conversion ratio was 98%.

At an appropriate time in the process, the average particle diameter ofthe core measured by Nicomp N300 dynamic light scattering equipment was320 nm, and the average particle diameter of the core-shell rubber resinlatex was 345 nm.

In addition, the particle size distribution of the produced core-shellrubber in the form of primary particles was measured, and the resultswere described in FIG. 1.

Thereafter, an antioxidant was added to the reactant, aggregated withmagnesium sulfate, and then dehydrated and dried to produce a core-shellrubber in an aggregated form.

Production Example 2: Production of Acrylic Crosslinked Particles

86 parts by weight of methyl methacrylate, 9 parts by weight of butylacrylate and 5 parts by weight of ethylene glycol dimethacrylate wereintroduced, 0.025 parts by weight of ethylenediaminetetrasodium acetate,0.003 parts by weight of ferrous sulfate, 0.1 parts by weight of sodiumformaldehyde sulfoxylate, 1 part by weight of sodium lauryl sulfate, 2.5parts by weight of alkenylsuccinic acid salt, 160 parts by weight ofion-exchanged water and 0.2 parts by weight of t-butyl hydroperoxidewere introduced, and then reacted at 65° C. for 6 hours to obtainacrylic crosslinked nanoparticles having an average particle size of 60nm.

Production Example 3: Production of Modified Urethane Resin

67 g of branched polypropylene glycol having an OH equivalent of 1,000,22.3 g of isophorone diisocyanate and 13.4 g of allylphenol and 0.1 g ofa tin catalyst were mixed in a nitrogen-substituted polymerizationreactor, and the reaction was performed at 75° C. to produce a modifiedurethane resin.

Production Example 4: Production of Structural Adhesive

The compositions of Examples and Comparative Examples containing thecomponents shown in Table 1 below in predetermined contents (weightratio: parts by weight) were prepared as adhesive materials.Specifically, the core-shell rubber conglomerates and the epoxy resinswere placed in a planetary mixer and mixed at 80° C. for 5 hours. Theappearance that the core-shell rubbers are dispersed in the epoxy resinis as shown in FIG. 2. Thereafter, the remaining components excluding‘the urethane resin, the curing agent and the catalyst’ were placed inthe planetary mixer and stirred at 80° C. for 3 hours. Finally, thetemperature was lowered to 40° C., ‘the urethane resin, the curing agentand the catalyst’ were put in the planetary mixer and mixed for 1 hour,and then the temperature was lowered to room temperature (about 23° C.)to terminate the kneading.

Method of Measuring Physical Properties

Impact Peel Strength

Five specimens were manufactured for each of Examples and ComparativeExamples, and an object weighing 45 kg was dropped freely at a rate of 2m/s at a height of 1.5 m in accordance with DIN ISO 11343, and theimpact peel strength (unit: N/mm) was measured at each of 80° C., 23° C.and −40° C. and the average value was taken.

In the case of the specimen, two cold rolled steel having a size of 90mm×25 mm×1.6 mm (length×width×thickness) and a strength of 440 MPa wereprepared, and the adhesive was applied to a predetermined area of thecold rolled steel so that the adhesive area of the cold rolled steel was25 mm×30 mm, and cured at 180° C. for 20 minutes. Using glass beads, thethickness of the adhesive layer was kept uniform at 0.2 mm. Themeasurement results were described in Table 2.

Shear Strength Experiment

For the specimens prepared in connection with Examples and ComparativeExamples, five shear strength measurements were performed in accordancewith DIN EN 1465 and the average value was taken. At this time, theshear strength (unit: Mpa) measurement was made under conditions of 10mm/min and 23° C.

In the case of the specimen, two cold rolled steel sheets having a sizeof 100 mm×25 mm×1.6 mm (length×width×thickness) and a strength of 440MPa were prepared, and the adhesive was applied to a predetermined areaof the cold rolled steel so that the adhesive area of the cold rolledsteel was 25 mm×10 mm, and cured at 180° C. for 20 minutes. Using glassbeads, the thickness of the adhesive layer was kept uniform at 0.2 mm.The measurement results were described in Table 2.

Experiment Results

TABLE 1 Comparative Example Example 1 1 2 3 4 First epoxy resin¹⁾ 20 2020 28 20 Second epoxy resin²⁾ 5 5 15 2 5 Third epoxy resin³⁾ 27 27 27 2727 Core-shell rubber⁴⁾ 12 — — 12 12 Core-shell rubber⁵⁾ — 12 12 — —Acrylic particle⁶⁾ 5 5 5 — 5 Urethane resin⁷⁾ 10 10 — 10 — Urethaneresin⁸⁾ — — — — 10 Mono epoxy resin⁹⁾ 1 1 1 1 1 Colorant¹⁰⁾ 0.05 0.050.05 0.05 0.05 Curing agent¹¹⁾ 5.6 5.6 5.6 5.6 5.6 Catalyst¹²⁾ 1 1 1 1 1CaCO₃ 10 10 10 10 10 Wollastonite 1 1 1 1 1 Fumed silica¹³⁾ 2 2 2 2 2Silane coupling agent¹⁴⁾ 0.35 0.35 0.35 0.35 0.35 1. First epoxyresin¹⁾: Bisphenol A-based epoxy resin (YD-128) having an epoxyequivalent of 200 or less 2. Second epoxy resin²⁾: Bisphenol A-basedepoxy resin (YD-011) having an epoxy equivalent of 300 or more 3. Thirdepoxy resin³⁾: Bisphenol F-based epoxy resin (YDF-170) having an epoxyequivalent of 200 or less 4. Core-shell rubber⁴⁾: Core-shell rubber ofProduction Example 1 5. Core-shell rubber⁵⁾: Paralloid EXL 2600 from DOW6. Acrylic particle⁶⁾: Acrylic crosslinked particle of ProductionExample 2 7. Urethane resin⁷⁾: Urethane resin of Production Example 3 8.Urethane resin⁸⁾: Huntzman DY965 9. Mono epoxy resin⁹⁾: NC513 fromCardolite 10. Colorant¹⁰⁾: Pigment violet 23 11: Curing agent¹¹⁾:Airproduct 1200 G 12: Catalyst¹²⁾: Evonik Amicure UR7/10 13: Fumedsilica¹³⁾: Cabo TS720 14: Silane coupling agent¹⁴⁾: GE Advanced materialA-187

TABLE 2 Comparative Example Example 1 1 2 3 4 Impact strength (−40° C.)28 5 X 15 4 Impact strength (23° C.) 39 34 28 36 32 Impact strength (80°C.) 38 31 29 33 32 Shear strength (23° C.) 33 32 33 30 30 X: the casewhere the stably measured value is not obtained because the measuredvalue is very low

1. An adhesive composition comprising: (a) one or more epoxy resins; (b) acrylic crosslinked particles comprising an alkyl (meth)acrylate unit and a polyfunctional acrylate unit; (c) a core-shell rubber in the form of secondary particles, wherein the secondary particles comprise two or more core-shell rubbers in the form of primary particles which are aggregated; (d) one or more epoxy curing agents; and (e) a urethane resin having a polyether structure.
 2. The adhesive composition according to claim 1, wherein the one or more epoxy resins are selected from a bisphenol A-based epoxy resin or a bisphenol F-based resin.
 3. The adhesive composition according to claim 2, wherein the one or more epoxy resins comprise at least one epoxy resin having a first epoxy equivalent of less than 300 and another epoxy resin having a second epoxy equivalent of 300 or more.
 4. The adhesive composition according to claim 3, wherein the adhesive composition comprises 15 parts by weight or more of the epoxy resins relative to a total content of the adhesive composition.
 5. The adhesive composition according to claim 1, wherein the acrylic crosslinked particles (b) have an average particle diameter in a range of 10 nm to 200 nm.
 6. The adhesive composition according to claim 1, wherein the two or more core-shell rubbers in the form of primary particles have an average particle diameter of 250 nm to 500 nm.
 7. The adhesive composition according to claim 1, wherein cores in the two or more core-shell rubbers in the form of primary particles have an average particle diameter of 180 to 495 nm.
 8. The adhesive composition according to claim 7, wherein the two or more core-shell rubbers in the form of primary particles have a ratio of a core particle diameter to a total particle diameter of core-shell particles satisfying 0.8 to 0.99.
 9. The adhesive composition according to claim 1, wherein the core-shell rubber has butadiene-based cores.
 10. The adhesive composition according to claim 1, wherein the adhesive composition comprises 5 to 35 parts by weight of the core-shell rubber in the form of secondary particles (c) based on a total content of the adhesive composition.
 11. The adhesive composition according to claim 1, wherein the urethane resin (e) having the polyether structure comprises a branched polyether polyol unit and a non-aromatic isocyanate unit.
 12. The adhesive composition according to claim 11, wherein the urethane resin (e) has at least one of isocyanate ends terminated with an amine-based compound, a phenol-based compound, an oxime-based compound, or a bisphenol-based compound.
 13. The adhesive composition according to claim 11, wherein the polyether polyol unit has an OH equivalent in a range of 300 to 2,000.
 14. The adhesive composition according to claim 13, wherein the polyether polyol unit has an OH equivalent in the range of 400 to 1,100.
 15. The adhesive composition according to claim 11, wherein the polyether polyol unit is branched polypropylene glycol.
 16. The adhesive composition according to claim 1, wherein the urethane resin (e) is included in a range of 5 to 25 parts by weight based on a total content of the adhesive composition.
 17. A structure comprising a cured product of the adhesive composition according to claim 1; and a base material in contact with the cured product.
 18. A method for producing a structure comprising: applying the adhesive composition according to claim 1 to a surface of a base material; and curing the adhesive composition applied to the surface of the base material. 